The underwhelming response to this thread forces me to add another message. The Fifth String (guitars, banjos, mandolins, etc.) in Berkeley has a weekly drop-in jam, lots of very good players, mostly tolerant of lesser talents--Thursdays from 7:30 to 9:30. The group forms in the banjo room and if many more than 10 people show up, a splinter moves into another room; very occasionally the group splits again into a third room. There is no charge, but most of the players have bought instruments there and buy strings, CDs, capos, etc., to make it worth it for the store to stay open. The repertoire is heavy on fiddle tunes, bluegrass ballads, and gospel songs, but other tastes squeeze in, also.

The Fifth String is located on Adoline Ave., across the street from the Ashby BART station.

This is the kind of thing I'm hoping other people will add to this thread; it would be particularly nice to find a similar place that also sells beer or coffee or other kinds of refreshments. --seed